Error tk

import pymysql
import tkinter as tk                # python 3
from tkinter import font as tkfont # python 3
#import Tkinter as tk     # python 2
#import tkFont as tkfont  # python 2


class SampleApp(tk.Tk):

    def __init__(self, *args, **kwargs):
        tk.Tk.__init__(self, *args, **kwargs)

        self.title_font = tkfont.Font(family='Helvetica', size=18, weight="bold", slant="italic")

        # the container is where we'll stack a bunch of frames
        # on top of each other, then the one we want visible
        # will be raised above the others
        container = tk.Frame(self)
        container.pack(side="top", fill="both", expand=True)
        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)

        self.frames = {}
        for F in (StartPage, PageOne):
            page_name = F.__name__
            frame = F(parent=container, controller=self)
            self.frames[page_name] = frame

            # put all of the pages in the same location;
            # the one on the top of the stacking order
            # will be the one that is visible.
            frame.grid(row=0, column=0, sticky="nsew")

        self.show_frame("StartPage")

    def show_frame(self, page_name):
        '''Show a frame for the given page name'''
        frame = self.frames[page_name]
        frame.tkraise()

        menu_bar = frame.menubar(self)
        self.configure(menu=menu_bar)


class StartPage(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        self.label_1 = tk.Label(parent, text="Username:")
        self.label_2 = tk.Label(parent, text="Password:")
        self.username = tk.Entry(parent, textvariable=tk.StringVar())
        self.username.focus_set()
        self.password = tk.Entry(parent, show="*", textvariable=tk.StringVar())
        self.sign_in = tk.Button(parent, text="Sign In", command=self.validation)
        self.label_1.grid(row=0)
        self.label_2.grid(row=1)
        self.username.grid(row=0, column=1, padx=3, pady=2)
        self.password.grid(row=1, column=1)
        self.sign_in.grid(row=2, column=1, rowspan=2)

    def validation(self, controller):
        u = str(self.username.get())
        p = str(self.password.get())
        conn = pymysql.connect(host="localhost", user="root", password="", db="e-library")
        c = conn.cursor()
        verify_user = "SELECT * from tblusers WHERE username = %s AND password = %s"
        c.execute(verify_user, (u, p))
        results = c.fetchall()

        if results:
            for i in results:
                print("Welcome " + i[1])
        else:
            print("Username or Password not recognized")


class PageOne(tk.Frame):

    def __init__(self, parent, controller):
        self.controller = controller
        self.parent = parent

    def menu_bar(self, root):
        main_menu = tk.Menu(root)
        file_menu = tk.Menu(main_menu)
        new_menu = tk.Menu(file_menu)
        main_menu.add_cascade(label='File', menu=file_menu)
        file_menu.add_cascade(label='New', menu=new_menu)
        file_menu.add_command(label='Register Student...', command=self.new_student)
        file_menu.add_command(label='Register Journal', menu=self.new_journal)
        return main_menu

    def new_student(self):
        print('I am a student')

    def new_journal(self):
        print('I am a journal')

'''
class PageTwo(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        label = tk.Label(self, text="This is page 2", font=controller.title_font)
        label.pack(side="top", fill="x", pady=10)
        button = tk.Button(self, text="Go to the start page",
                           command=lambda: controller.show_frame("StartPage"))
        button.pack()
'''

if __name__ == "__main__":
    app = SampleApp()
    app.mainloop()